1. Field of the Invention
The present invention relates generally to an antenna, and more particularly to a multi-band antenna used in an electrical device.
2. Description of the Prior Art
In recent years, portable wireless communication devices are becoming increasingly popular. For the design of the wireless communication device, an antenna used with it for transmitting and receiving electromagnetic waves is an important factor should be taken into account. The antenna may be mounted out of or in the device. In general use, the antenna is built-in arranged to save space and increase convenience. Considering the miniaturization trend of the wireless communication devices, the size of the antenna should be accompanylingly reduced in order to be assembled in the limit space of the communication device.
Moreover, among present wireless technologies, Bluetooth running in 2.4 GHz, IEEE 802.11b/g running in 2.4 GHz and IEEE 802.11a running in 5 GHz are prevailing and dominant. In response to the wide applications of the frequency, there is an increasing demand to make one communication device to support two or more frequencies.
To make the miniaturized antenna supporting two or more working frequencies becomes a hot R&D issue. Many antennas have been developed in prior arts to address the issue, such as microstrip antennas, antennas with high dielectric constant, planar inverted-F antennas, combinations of loop antenna and slot antenna, small size patch antennas and the like.
U.S. Patent Application No. 2004/0017319 discloses a conventional multi-band planar inverted-F antenna with low profile and small size. The antenna is formed on a frame of a notebook computer. The antenna comprises a dielectric substrate, a first and a second radiating metal strips formed on a same surface of the substrate and extending in a same direction, and a ground plane. However, the dielectric substrate of the antenna will introduce insertion loss, which adversely affects the antenna gain.
Hence, in this art, a dual-band antenna with low profile and small size to overcome the above-mentioned disadvantages of the prior arts will be described in detail in the following embodiments.